Crawling and Sitting

So before we left for Bend, when Wynn was exactly 6 months old, he'd been getting from one side of a room to another by rolling and scooching and.....we're not sure exactly how.  We'd just look away, look back and he was in a different spot.  But when we first got to Oregon, he did the army crawl, pulling his body with his arms.  He all of the sudden got really sturdy sitting up by himself too.  A few days later he crawled officially with Tim and I alone in a room watching him! Good boy.  Is it just me or is this all moving really quickly?  He now crawls all over and sits without assistance.  I don't even need to put pillows behind him.  He and Oly sit in the living room and play legos together for 30 minutes at a time